We've had several of these reports already. Our investigation showed that an update of Acrobat DC causes the toolbars of all third party plugins to disappear (so plugins from other vendors are also affected). We've found a way to bring back the toolbars, so you can use this as a workaround until Adobe permanently fixes the issue in Acrobat.

We've also had reports that the issue can come back after the steps in the article, so you might have to do it again. I would also advise that people having the issue report it to Adobe so they are aware how many people are affected, this may result in a higher priority for the investigation of the issue.

We have more information on the issue. It only happens when "Open documents as new tabs in the same Window (requires restart)" in the General Category of the Acrobat preferences is disabled. When you enable this setting and restart Acrobat the issue is avoided.